Fix readthedocs errors, update documentation

[apcraig]

PR checklist

• [X] Short (1 sentence) summary of your PR: Fix documentation, new errors trapped by readthedocs
• [X] Developer(s): apcraig
• [X] Suggest PR reviewers from list in the column to the right.
• [X] Please copy the PR test results link or provide a summary of testing completed below. no testing done
• How much do the PR code changes differ from the unmodified code?
  • [X] bit for bit
  • [ ] different at roundoff level
  • [ ] more substantial
• Does this PR create or have dependencies on CICE or any other models?
  • [ ] Yes
  • [X] No
• Does this PR add any new test cases?
  • [ ] Yes
  • [X] No
• Is the documentation being updated? ("Documentation" includes information on the wiki or in the .rst files from doc/source/, which are used to create the online technical docs at https://readthedocs.org/projects/cice-consortium-cice/.)
  • [X] Yes
  • [ ] No, does the documentation need to be updated at a later time?
    • [ ] Yes
    • [ ] No
• [X] Please provide any additional information or relevant details below:

There seems to have been a problem with unicode character representing a minus sign. Fixing that seems to fix the pdf generation.

[apcraig]

I will merge this once GHActions checks are done and see if it fixes the documentation and doc badge. I tested the fix in readthedocs, but will have to see whether it really is the fix.

[apcraig]

The readthedocs log files helped find the problem. But yes, not easy to find.